1. Field of the Invention
The present invention relates to a stopper for stopping the rotation of a bobbin case in a lock stitch sewing machine.
2. Description of the Prior Art
In a known vertical full rotation shuttle device, a bobbin case retaining member is fixed on a sewing machine body in order to arrest the rotation of a bobbin case. After a needle thread and a bobbin thread are tied to make a loop, the loop must pass through the retaining member and the contacting surface part of the bobbin case. The mutual contact pressure at this contacting position is unstable, and the tension of the needle thread fluctuates, which results in uneven thread tightening.
This problem conventionally has been solved by an opener mechanism, wherein when the needle thread passes through the contact position, the bobbin case is slightly moved angularly by a collision piece in a direction opposite to the direction of rotation of the loop taker, and a free space is formed for a moment in the contact position, so that the needle thread may pass through the space smoothly. In this method, however, since the bobbin case is angularly moved by the collision piece so that a free space may be produced between the retaining member and the bobbin case, noise due to the collision of the collision piece and the bobbin case, and of the retaining member and the bobin case cannot be avoided.
It is an object of the present invention to provide a stopper device for lock stitch sewing machine which is capable of passing the needle thread smoothly and quietly between the bobbin case and the retaining member.